Since 1995, word mavens have been wowed by the work of Dr. Robert Beard. Beard's "Web of Online Dictionaries" is now part of yourDictionary.com, an amazing site dedicated to the study of words. Launched in 1999, yourDictionary.com features an index of 1300+ dictionaries in more than 230 languages.
Other word tools abound, including 80 categories of specialized dictionaries covering everything from advertising to travel, and grammars for everything from Akkadian to Wolof (English is in there, too.) In addition to a growing collection of articles penned by linguists for word-o-philes, there's a lot of fun stuff. Check out the word of the day, word games and a European language translator, to name a few. You can also customize your browser by placing YD's handy Lookup Button on your toolbar (powered by Merriam-Websters' Collegiate). One of the most intriguing aspects of the site is the Endangered Language Repository, which aims to acquire dictionaries and grammars of dying languages to help preserve cultures and linguistic research. If you use words, you'll definitely want to bookmark this site.